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Antennas and Propagation, IEEE Transactions on

Issue 12 • Date Dec. 2001

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Displaying Results 1 - 25 of 42
  • Foreword to the special issue on millennium day of diffraction seminars

    Publication Year: 2001 , Page(s): 1610 - 1611
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    Freely Available from IEEE
  • Author index

    Publication Year: 2001 , Page(s): 1884 - 1891
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  • Subject index

    Publication Year: 2001 , Page(s): 1891 - 1916
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  • Diffraction by a line of curvature jump (a special case)

    Publication Year: 2001 , Page(s): 1618 - 1623
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    We consider the problem of diffraction of a short-wave field by a cylindrical body with the boundary that consists of a half plane and a convex-cylindrical surface jointed together along a straight line. The main feature of the problem under consideration is the jump of curvature of the boundary on the line. The problems with the Dirichlet, Neumann, and impedance boundary conditions are considered. The main terms of asymptotic expansion of wave fields for the problems are constructed View full abstract»

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  • Synthesis of large low-redundancy linear arrays

    Publication Year: 2001 , Page(s): 1881 - 1883
    Cited by:  Papers (12)
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    Aperture synthesis interferometric radiometers can overcome mass, weight and mechanical scan limitations of present-day radiometers. A full antenna array is "thinned" by eliminating selected antennas, while keeping all possible antenna separations. This paper describes a new technique for the direct synthesis of low-redundancy large arrays, consisting in growing small arrays by inserting a seed repeatedly. This technique has achieved the largest thinned arrays with the least redundancy reported in the literature View full abstract»

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  • Theory and analysis of leaky coaxial cables with periodic slots

    Publication Year: 2001 , Page(s): 1723 - 1732
    Cited by:  Papers (57)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (365 KB) |  | HTML iconHTML  

    Frequency band and coupling loss are the two important parameters of leaky coaxial cables with periodic slots. The frequency band can be predicted by analyzing the arrangement of the slots on the outer shield of the cable, but the coupling loss is not so easy to determine by classical methods. In this paper, the finite-difference time-domain (FDTD) method is used to calculate the electric field distribution in the slot cut in the outer conductor of the coaxial cable. The dyadic Green's function is then used to calculate the radiation field of the equivalent surface magnetic current densities. By these two methods, the coupling losses of the leaky coaxial cables with different periods, sizes and shapes of the slots can be accurately obtained. Some results in this paper were verified by the experimental results of leaky coaxial cables designed for railway mobile communications with a frequency band of 100-500 MHz View full abstract»

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  • Diffraction by an anisotropic dielectric half-plane: a uniform asymptotic PO solution

    Publication Year: 2001 , Page(s): 1624 - 1627
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (108 KB) |  | HTML iconHTML  

    A uniform solution is proposed to, describe the diffraction by a penetrable anisotropic dielectric halfplane illuminated at normal incidence by an electromagnetic plane wave. Resorting to second-order boundary conditions on a sheet simulating a special type of anisotropic dielectric thin layer, a physical optics (PO) approximation for the induced electric and magnetic surface currents is derived. Then, a uniform asymptotic evaluation of the corresponding radiation integral provides the diffracted field in terms of the standard transition function relevant to the uniform theory of diffraction. The effectiveness of the solution is proved by many numerical tests View full abstract»

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  • A crack identification microwave procedure based on a genetic algorithm for nondestructive testing

    Publication Year: 2001 , Page(s): 1812 - 1820
    Cited by:  Papers (28)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (235 KB) |  | HTML iconHTML  

    This paper is aimed at exploring the possibility of using a microwave approach based on a genetic algorithm to detect a defect inside a known host object. Starting from the knowledge of the scattered field, the problem solution is recast as a two-step procedure. After defining a cost function depending on the geometric parameters of the crack, a minimization procedure based on a hybrid-coded genetic algorithm is applied. The influence of the noise as well as of the geometry of the defect on the crack detection and reconstruction is investigated. Moreover, the numerical effectiveness of the iterative approach is examined View full abstract»

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  • Scattering from surface waves on finite FSS

    Publication Year: 2001 , Page(s): 1782 - 1793
    Cited by:  Papers (7)
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    This paper discusses the presence of surface waves on periodic structures in general and on frequency selective surfaces (FSS) in particular. While certain types of surface waves can exist on infinite as well as finite periodic structures, this investigation centers around the types that can exist only on finite FSS. Radiation caused by these surface waves may lead to a significant scattering increase in the backscatter as well as the bistatic directions. Thus, this paper is of both theoretical and practical interest View full abstract»

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  • Admittance of transverse waveguide slots in cylindrical structures

    Publication Year: 2001 , Page(s): 1733 - 1738
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (108 KB) |  | HTML iconHTML  

    The self and mutual admittances of transverse slots in arbitrary conducting cylindrical structures are computed. The analysis is performed in the spectral domain, where all fields and currents have been Fourier transformed along the structure. There are, however, no transformations in the transverse directions. A system of integral equations for cylindrical structures are formulated and solved with the moment method. The induced currents on the structure can thus be determined and used to compute the spectral self and mutual admittance of the slots. The spectral admittance is inverse transformed and included in the overall slot antenna analysis. The analysis is rigorous with trigonometric basis function expansions at the inner and outer slot apertures. Computed results on scattering parameters in the waveguide show good agreement with measured data View full abstract»

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  • Scattering by a groove in a conducting plane-a PO-MoM hybrid formulation and wavelet analysis

    Publication Year: 2001 , Page(s): 1807 - 1811
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (116 KB)  

    A novel method is presented to solve the two-dimensional (2-D) problem of scattering of an electromagnetic plane wave by a groove in a perfectly conducting infinite plane. In this method, the unknown induced current is expressed in terms of the known physical optics solution of the unperturbed problem of scattering by an infinite conducting plane plus a yet to be determined localized correction current placed in the vicinity of the groove. It is then shown that a good approximation of the induced current can be obtained using only a few dominant functions in the wavelet expansion of the correction current. Moreover, the same set of dominant wavelet functions serves the purpose of approximating the induced current at different angles of incidence. A numerical example demonstrates these various features of the proposed method of solution View full abstract»

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  • High-frequency scattering by an isorefractive wedge with the parabolic equation method

    Publication Year: 2001 , Page(s): 1628 - 1632
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    The parabolic equation (PE) method is applied to the problem of the high-frequency scattering from a diaphanous wedge, that is, a wedge made of a material which is isorefractive with respect to the surrounding medium, illuminated by a plane wave or by a line current parallel to the edge. The proposed approach is able to handle any wedge aperture and incidence angle and presents some novelties that allows overcoming the problems arising in the numerical solution of the parabolic equation applied to penetrable wedges View full abstract»

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  • Considerations on performance evaluation of cavity-backed slot antenna using the FDTD technique

    Publication Year: 2001 , Page(s): 1712 - 1717
    Cited by:  Papers (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (118 KB)  

    The finite-difference time-domain (FDTD) method is considered a versatile and efficient tool for the solution of Maxwell's equations in complex structures for any time dependence. We show an antenna feed model suitable for performance evaluation of a cavity-backed slot antenna using the FDTD technique. The gap voltage and the coaxial feed models are examined, and their input characteristics and absolute gains are compared. Analytical results show that the input characteristics are estimated with fewer time steps for the coaxial model than for the conventional gap voltage model. Furthermore, we show how to calculate absolute gains and radiation patterns using the coaxial model and a sinusoidal voltage source at the desired frequency. The computed results of the absolute gain converge after the fifteenth period of the voltage source for the coaxial model and are in good agreement with the experimental results. On the other hand, the absolute gain is observed to fluctuate when the gap voltage model is used. The performance evaluation and comparison reveals that the coaxial model is an appropriate feed model for use in the analysis of the performance of the cavity-backed slot antenna using the FDTD technique. The good agreement of the FDTD results with the experimental measurements demonstrates the effectiveness of the model and the method proposed View full abstract»

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  • Direction-finding methods for cyclostationary signals in the presence of coherent sources

    Publication Year: 2001 , Page(s): 1821 - 1826
    Cited by:  Papers (13)
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    By exploiting the signal cyclostationarity, conjugate cyclic MUSIC presented by Gardner (1994), has been shown to be effective in performing signal-selective direction finding. However, a direct application of conjugate cyclic MUSIC in the presence of coherent signals of interest (SOIs) will result in ambiguity. To tackle the drawback of conjugate cyclic MUSIC, we present a scheme called the Hankel approximation method (HAM) in conjunction with conjugate cyclic MUSIC to cope with the performance deterioration due to coherent SOIs for a uniform linear array. Theoretical analysis shows that at least 2K sensor elements are required to resolve K coherent SOIs. Making use of the forward/backward (F/B) technique presented by Pillai and Kwon (1989), F/B HAM is further developed, which requires [3K/2] sensor elements to decorrelate K coherent SOIs, where [x] represents the integer part of x. Several simulation examples are also presented for illustrating the effectiveness of the proposed methods View full abstract»

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  • Rigorous and efficient full-wave analysis of trapezoidal patch antennas

    Publication Year: 2001 , Page(s): 1773 - 1776
    Cited by:  Papers (8)
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    A rigorous full-wave analysis in the spectral domain for trapezoidal patch antennas is presented. Particularly, a new set of entire domain basis functions for an efficient implementation of the method of moments (MoM) is carried out by properly imposing the boundary conditions. The simulated results obtained through the presented method are compared to the measurements showing a good agreement. Finally, a parametric analysis of the main antenna features (matching, radiation pattern, cross-polarization levels) is also carried out View full abstract»

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  • Range sidelobe suppression technique for coherent ultra wide-band random noise radar imaging

    Publication Year: 2001 , Page(s): 1836 - 1842
    Cited by:  Papers (21)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (153 KB) |  | HTML iconHTML  

    When applied in airborne imaging surveillance, ultra wide-band (UWB) random noise radars have their special merits. Because of the randomness and the ultrawide bandwidth of the transmit and receive signals, such radars can be used for covert detection and identification, and are immune from hostile detection and jamming while preserving very high range resolution. However, the images are plagued with artifacts caused by high range sidelobes. In this paper, a new technique for the range sidelobe suppression of UWB random noise radar, which combines median and apodization filtering, is proposed. Computational and experimental results show the effectiveness of this image enhancement procedure View full abstract»

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  • Analysis of the zonal and rectangular slots on a conducting spherical cavity

    Publication Year: 2001 , Page(s): 1739 - 1745
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (203 KB) |  | HTML iconHTML  

    The zonal slot cut on a conducting spherical cavity is analyzed rigorously. The slot is excited asymmetrically, which excites higher order azimuthal modes. The Green's function approach is used to formulate an integral equation for the magnetic current in the slot, which is solved using the moment method (MoM). New recurrence formulas are derived so that within their stable region the admittance integrals can be evaluated without the need for any numerical integration. In this case, the solution is very easy to implement with extremely short computation time. The effects of the latitude angle on the peak resistance and percentage bandwidth are investigated. Furthermore, the cavity resonance modes and their degeneracy are examined by plotting the expansion coefficients of the magnetic current. In addition, the problem of a rectangular slot in the nonequatorial plane is also studied. Measurements are carried out and good agreement between theory and experiment is obtained View full abstract»

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  • Shaping of flat-topped element patterns in an array of slow-wave strip structures excited by parallel-plate waveguides

    Publication Year: 2001 , Page(s): 1763 - 1768
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (146 KB) |  | HTML iconHTML  

    A two-dimensional (2-D) model of a corrugated-rod antenna array in the form of an infinite periodic array of finite slow-wave strip structures arranged above the apertures of two-or three-mode parallel-plate waveguides excited by TEM modes is analyzed. The formulated problem is solved by the method of matching the waveguide and Floquet modes on the waveguide apertures in combination with the Galerkin method for calculation of the currents on the strips. The geometrical parameters of the strip structures are optimized for shaping the flat-topped element patterns. It is shown that high quality of the flat-topped patterns in the element spacing range from 0.65 to 1.3 of wavelength is achieved if the excitation of the optimized structures is performed using the second and third reflected waveguide modes returned back to the apertures with the corresponding optimum phases. The presented examples also show that the shape of the obtained patterns keeps well at least in a 10% frequency band View full abstract»

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  • Attenuation and backscatter from a derived two-dimensional duststorm model

    Publication Year: 2001 , Page(s): 1703 - 1711
    Cited by:  Papers (18)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (236 KB) |  | HTML iconHTML  

    Fundamentals of attenuation and radar backscatter through duststorms are reviewed. A duststorm is modeled as circularly symmetric having a visibility with a minimum at its center (e.g., maximum mass loading) and which exponentially increases radially to a fixed maximum visibility threshold level (minimum mass loading). This model enables the convenient calculation of the two dimensional (2-D) structure of radar backscatter and path attenuation. As an example, the parameters of the exponential function describing the visibility distribution for a particular duststorm was derived using measurements made in the Sudan by other investigators operating a 10.5 GHz, 25 km link. A comparison of the calculated and measured attenuation time-series showed relatively close agreement. Both attenuation levels and backscatter levels due to even intense duststorms are expected to be relatively small for frequencies up to 10 GHz. For example, the peak attenuation for the duststorm that contained visibilities smaller than 2 m was less than 6.5 dB. Modeled backscatter due to this duststorm gave levels smaller than that obtained by an equivalent rainrate of 0.6 mm/h. Although the calculations were obtained for X-band, they may be extended to higher frequencies. Frequency scaling at 37 GHz, for example, showed a peak equivalent path attenuation level of at least 26.6 and 48 dB under varying assumptions View full abstract»

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  • A novel hybridization of higher order finite element and boundary integral methods for electromagnetic scattering and radiation problems

    Publication Year: 2001 , Page(s): 1794 - 1806
    Cited by:  Papers (47)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (315 KB) |  | HTML iconHTML  

    A novel hybridization of the finite element (FE) and boundary integral methods is presented for an efficient and accurate numerical analysis of electromagnetic scattering and radiation problems. The proposed method derives an adaptive numerical absorbing boundary condition (ABC) for the finite element solution based on boundary integral equations. Unlike the standard finite element-boundary integral approach, the proposed method is free of interior resonance and produces a purely sparse system matrix, which can be solved very efficiently. Unlike the traditional finite element-absorbing boundary condition approach, the proposed method uses an arbitrarily shaped truncation boundary placed very close to the scatterer/radiator to minimize the computational domain; and more importantly, the method produces a solution that converges to the true solution of the problem. To demonstrate its great potential, the proposed method is implemented using higher order curvilinear vector elements. A mixed functional is designed to yield both electric and magnetic fields on an integration surface, without numerical differentiation, to be used in the calculation of the adaptive ABC. The required evaluation of boundary integrals is carried out using the multilevel fast multipole algorithm, which greatly reduces both the memory requirement and CPU time. The finite element equations are solved efficiently using the multifrontal algorithm. A mathematical analysis is conducted to study the convergence of the method. Finally, a number of numerical examples are given to illustrate its accuracy and efficiency View full abstract»

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  • Plane wave, pattern subtraction, range compensation

    Publication Year: 2001 , Page(s): 1843 - 1851
    Cited by:  Papers (19)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (228 KB) |  | HTML iconHTML  

    Plane wave, pattern subtraction (PWPS) range compensation improves the performance of far field and compact, antenna pattern measurement systems by compensating errors introduced by antenna measurement facility (range) imperfections. The range-field model consists of a plane wave that represents an ideal range field plus a selectable number of plane waves representing range field imperfections. The error patterns introduced by the undesired range-field plane waves are estimated and subtracted from the measured pattern to produce a compensated pattern. This compensated pattern is used to obtain an improved estimate of the error patterns. This iterative procedure is continued until the compensation algorithm converges. The antenna measurement range field is measured on the surface of a sphere enclosing the test zone, and a plane-wave model of this range field is constructed View full abstract»

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  • Wave emission from an open-ended cylindrical channel in a cold magnetoplasma

    Publication Year: 2001 , Page(s): 1645 - 1648
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (121 KB) |  | HTML iconHTML  

    We study wave emission from a transmitting system consisting of a magnetic-field-aligned cylindrical plasma channel of enhanced density and a loop antenna immersed in it. An ambient medium is assumed to be a cold uniform magnetoplasma. It is found that when the plasma density in the near-antenna zone increases, the total power radiated from the antenna increases considerably due to the efficient excitation of guided modes on the channel. We consider the emission of these modes from the channel end, assuming that the plasma density in the channel decreases gradually with distance from the loop. It is shown that under ionospheric conditions this transmitting system can be useful for improving the antenna coupling to VLF waves of the ambient plasma View full abstract»

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  • Atmospheric transmission at microwaves (ATM): an improved model for millimeter/submillimeter applications

    Publication Year: 2001 , Page(s): 1683 - 1694
    Cited by:  Papers (67)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (297 KB) |  | HTML iconHTML  

    We present a model of the longwave atmospheric spectrum that improves in many respects widely used older models such as the microwave propagation model (MPM), since it is based on broadband measurements and calculations. According to our data, the model is fully applicable from 0 to 2 THz while including lines up to 10 THz. Its primary goal is to simulate the millimeter/submillimeter region accessible from the ground (frequencies up to ~2 THz at most, with a few windows between 1 and 2 THz accessible only under exceptional conditions at very dry sites). Line-by-line calculations of the absorption are performed using a line database generated from the latest available spectroscopic constants for all relevant atmospheric species. The collisional line widths are obtained from published laboratory data. The excess of absorption in the longwave range that cannot be explained by the line spectrum is modeled by introducing two different continuum-like terms based on FTS measurements between 170 and 1100 GHz: collision-induced absorption of the dry atmosphere due to transient dipoles in symmetric molecules (N 2 and O2) and continuum-like water vapor opacity. All H2O lines up to 10 THz are included in order to correctly account for the entire H2O far-wing opacity below 2 THz for a given line-shape. Hence, this contribution does not need to be part of a pseudocontinuum term below that frequency cutoff (still necessary, as shown in this paper) in contrast to other models used to date. Phase delays near H2O and O2 resonances are also important for ground-based astronomy since they affect interferometric phase. The frequency-dependent dispersive phase delay function is formally related to the absorption line shape via the Kramers-Kronig dispersion theory, and this relation has been used for modeling those delays. Precise calculations of phase delays are essential for the future Atacama large millimeter array (ALMA) project. A software package called atmospheric transmission at microwaves (ATM) has been developed to provide the radioastronomy and aeronomy communities with an updated tool to compute the atmospheric spectrum in clear-sky conditions for various scientific applications. We use this model to provide detailed simulations of atmospheric transmission and phase dispersion for several sites suitable for submillimeter astronomy View full abstract»

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  • Plane-wave scattering-matrix formulation for two interfaces plus a scatterer (uniplanar case)

    Publication Year: 2001 , Page(s): 1852 - 1861
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    Kern's plane-wave scattering-matrix formulation is extended to treat the case of two interfaces plus a scatterer imbedded in the second region. This formulation can treat different shapes for the scatterer and only requires two different evaluations depending upon the location of the observer: 1) in the near field, a two-dimensional (2-D) fast Fourier transform (FFT) (one-dimensional (1-D) FFT is treated by an analytical integration), and 2) in the far-field an asymptotic evaluation of the integral. These two regimes are in contrast to the Sommerfeld integral approximations where different approximations are required for various parameter ranges (quasistatic, saddle-point evaluation for the radiation field, saddle point evaluation for the surface field when the saddle point is near a pole, and the lateral wave field evaluated using a uniform asymptotic evaluation for the integrals) View full abstract»

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  • High-frequency Green's function for a semi-infinite array of electric dipoles on a grounded slab .I. formulation

    Publication Year: 2001 , Page(s): 1667 - 1677
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (314 KB) |  | HTML iconHTML  

    A uniform, high-frequency solution is presented for the electromagnetic field radiated at finite distance by a semi-infinite array of elementary electric dipoles placed on an infinite grounded dielectric slab. This solution is useful for the efficient analysis of printed arrays. The field is represented in terms of a series encompassing propagating and evanescent truncated Floquet waves together with their corresponding diffracted rays, which arise from the edge of the array. The high-frequency formulation also includes surface and leaky wave contributions excited at the array edge. The diffracted waves contain discontinuities which compensate the disappearance of surface, leaky and truncated Floquet waves at their pertinent shadow boundaries View full abstract»

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IEEE Transactions on Antennas and Propagation includes theoretical and experimental advances in antennas.

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Editor-in-Chief                                                 Kwok W. Leung